Overactive Bladder and Incontinence in the Absence of the BK Large Conductance Ca2+-activated K+ Channel

Meredith, Andrea L.; Thorneloe, Kevin S.; Werner, Matthias; Nelson, Mark T.; Aldrich, Richard W.

doi:10.1074/jbc.m405621200

Cited by 310 publications

(390 citation statements)

References 29 publications

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“…Previous investigations established that the BK Ca channel has a central role in the modulation of nonvascular (26,37) and vascular contractility (18,28), as well as in the corpus cavernosum (11,12,25). The suggested mechanism of BK Ca channel function is linked to the hyperpolarization of smooth muscle cells and a concomitant decrease in transmembrane Ca 2ϩ flux through L-type VDCC (7,18).…”

Section: Discussionmentioning

confidence: 99%

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Hypercontractility and impaired sildenafil relaxations in the BK_Cachannel deletion model of erectile dysfunction

Werner

Meredith

Aldrich³

et al. 2008

American Journal of Physiology-Regulatory, Integrative and Comp

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Werner ME, Meredith AL, Aldrich RW, Nelson MT. Hypercontractility and impaired sildenafil relaxations in the BK Ca channel deletion model of erectile dysfunction. Am J Physiol Regul Integr Comp Physiol 295: R181-R188, 2008. First published May 14, 2008 doi:10.1152/ajpregu.00173.2008.-Erectile dysfunction (ED) can be elicited by a variety of pathogenic factors, particularly impaired formation of and responsiveness to nitric oxide (NO) and the downstream effectors soluble guanylate cyclase (sGC) and cGMP-dependent protein kinase I (PKGI). One important target of PKGI in smooth muscle is the large-conductance, Ca 2ϩ -activated potassium (BKCa) channel. In our previous report (42), we demonstrated that deletion of the BK Ca channel in mice induced force oscillations and led to reduced nerve-evoked relaxations and ED. In the current study, we used this ED model to explore the role of the BK Ca channel in the NO/sGC/PKGI pathway. Electrical field stimulation (EFS)-induced contractions of corpus cavernosum smooth muscle strips were significantly enhanced in the absence of BK Ca channel function. In strips precontracted with phenylephrine, EFS-induced relaxations were converted to contractions by inhibition of sGC, and this was further enhanced by loss of BK channel function. Sildenafil-induced relaxations were decreased to a similar extent by inhibition of sGC or BK Ca channels. At concentrations Ͼ1 M, sildenafil caused relaxations independent of inhibition of sGC or BK Ca channels. Sildenafil did not affect the enhanced force oscillations that were induced by the loss of BK Ca channel function. Yet, these oscillations could be completely eliminated by blocking L-type voltage-dependent Ca 2ϩ channels (VDCCs). These results suggest that therapeutically relevant concentrations of sildenafil act through cGMP and BK Ca channels, and loss of BKCa channel function leads to hypercontractility, which depends on VDCCs and cannot be modified by the cGMP pathway. smooth muscle; calcium-activated potassium channel; mouse ERECTILE DYSFUNCTION (ED) is described as the persistent inability to achieve or maintain an erection sufficient for satisfactory sexual performance (44). It affects 30 million men in the United States (5), and its prevalence increases with age and diseases like diabetes and hypertension (4,24,31). Erectile function and a proper penile erection occurs in response to nerve stimulation and the release of nitric oxide (NO) from parasympathetic nonadrenergic-noncholinergic (NANC) nerves as well as from the vascular endothelium (2,13,16,27). In mice, the NO-producing enzyme NO synthase has been found in the dorsal penile nerve and its branches in the mouse penis (9) as well as in intrinsic nerves of the erectile tissue (14). The majority of NO effects are mediated through the soluble guanylate cyclase (sGC) and its product, cGMP (2,8,16,33). cGMP acts as a modifying agent on ion channels, phosphodiesterases, and protein kinases (19). One of the protein kinases, the cGMP-dependent protein kinase I (PKGI), phosphorylat...

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Section: Discussionmentioning

confidence: 99%

“…Slo Ϫ/Ϫ mice were generated as previously published (26). All procedures performed in the course of this study were approved by the Office of Animal Care Management at the University of Vermont.…”

Section: Methodsmentioning

confidence: 99%

Hypercontractility and impaired sildenafil relaxations in the BK_Cachannel deletion model of erectile dysfunction

Werner

Meredith

Aldrich³

et al. 2008

American Journal of Physiology-Regulatory, Integrative and Comp

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“…[1][2][3] In bladder smooth muscle, BK channels are activated by both the influx of Ca 2+ across the membrane and the release of Ca 2+ from intracellular stores and are responsible for the rapid repolarisation phase of the action potential. Thus, BK channels help limit the excitability of bladder smooth muscle and consequently reduce its contractile behaviour.Meredith et al, [4] elegantly illustrated the importance of BK channels in controlling bladder contractility by demonstrating that mutant mice, which lack the BKα subunits, have overactive bladders and are functionally incontinent.It is clear from the above studies that BK channels offer a promising target for the treatment of urinary incontinence caused by overactive bladder (OAB). In this study, we have synthesised a new family of BK channel openers, termed the GoSlo-SR family, that may form scaffold molecules for future development in the treatment of this disease.…”

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Structure–Activity Relationships of a Novel Group of Large‐Conductance Ca²⁺‐Activated K⁺ (BK) Channel Modulators: The GoSlo‐SR Family

et al. 2012

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Main TextLarge-conductance Ca 2+ -activated K + (BK) channels contribute to the repolarisation or hyperpolarisation of a wide variety of tissues including bladder and urethral smooth muscles. [1][2][3] In bladder smooth muscle, BK channels are activated by both the influx of Ca 2+ across the membrane and the release of Ca 2+ from intracellular stores and are responsible for the rapid repolarisation phase of the action potential. Thus, BK channels help limit the excitability of bladder smooth muscle and consequently reduce its contractile behaviour.Meredith et al., [4] elegantly illustrated the importance of BK channels in controlling bladder contractility by demonstrating that mutant mice, which lack the BKα subunits, have overactive bladders and are functionally incontinent.It is clear from the above studies that BK channels offer a promising target for the treatment of urinary incontinence caused by overactive bladder (OAB). In this study, we have synthesised a new family of BK channel openers, termed the GoSlo-SR family, that may form scaffold molecules for future development in the treatment of this disease. The predominant cause of OAB is the uncontrolled, inappropriate contraction of the bladder smooth muscle, which increases intravesicle pressure above urethral closure pressure causing urine leakage. [5] The current 'gold standard' therapeutic treatment (anticholinergics) for overactive bladder has compliance rates of <30%, due to unwanted side effects including chronic constipation and dry mouth. [6] Consequently, the pharmaceutical industry has invested significantly in trying to target smooth muscle function by developing novel BK channel modulators to help treat disorders such as urinary incontinence. [6][7][8][9][10] Although a large number of chemically diverse BK channel openers have already been developed, [8,9] only a few studies [11][12][13] have focused on examining the effects of these compounds across a wide voltage range to include physiological potentials (~−100 mV to 0 mV). [10][11][12] Instead, the majority of studies have focused on the ability of compounds to open channels only at potentials some 50 to 100 mV more positive than a cell is ever likely to encounter in vivo. It appears that the majority of BK channel openers developed to date would have little effect at physiological membrane potentials and this may explain their poor efficacy in clinical trials [7] and subsequent failure to progress to market.In this study, we have examined the effects of the GoSlo-SR family of molecules across a wide range of potentials (from −100 mV to +150 mV). In addition, we have chosen to measure efficacy of these BK channel openers by calculating the shift in the voltage required to half maximally activate the channels (ΔV1/2). We have previously used this approach to demonstrate that 10 µM Cibacron Blue (Reactive Blue 2, RB2, see Figure 1A) activated BK channels recorded from bladder smooth muscle cells with ΔV1/2 of~−50 mV. [11] However, little is known about the minimal structure necessary to ret...

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“…KCNMA1 ͉ acylation ͉ protein kinase A ͉ maxi-K L arge conductance calcium-and voltage-gated potassium (BK) channels are potently regulated by protein phosphorylation (1) and are important determinants of neuronal, cardiovascular, endocrine, and epithelial function where channel dysfunction may lead to major disorders such as hypertension (2,3), ataxia (4), epilepsy (5,6), and incontinence (7). BK channels are potently regulated by phosphorylation, and several putative phosphorylation motifs on the pore-forming ␣-subunit have been identified (8)(9)(10)(11)(12).…”

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confidence: 99%

Palmitoylation gates phosphorylation-dependent regulation of BK potassium channels

Tian

Jeffries

McClafferty

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

105

180

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Large conductance calcium-and voltage-gated potassium (BK) channels are important regulators of physiological homeostasis and their function is potently modulated by protein kinase A (PKA) phosphorylation. PKA regulates the channel through phosphorylation of residues within the intracellular C terminus of the poreforming ␣-subunits. However, the molecular mechanism(s) by which phosphorylation of the ␣-subunit effects changes in channel activity are unknown. Inhibition of BK channels by PKA depends on phosphorylation of only a single ␣-subunit in the channel tetramer containing an alternatively spliced insert (STREX) suggesting that phosphorylation results in major conformational rearrangements of the C terminus. Here, we define the mechanism of PKA inhibition of BK channels and demonstrate that this regulation is conditional on the palmitoylation status of the channel. We show that the cytosolic C terminus of the STREX BK channel uniquely interacts with the plasma membrane via palmitoylation of evolutionarily conserved cysteine residues in the STREX insert. PKA phosphorylation of the serine residue immediately upstream of the conserved palmitoylated cysteine residues within STREX dissociates the C terminus from the plasma membrane, inhibiting STREX channel activity. Abolition of STREX palmitoylation by site-directed mutagenesis or pharmacological inhibition of palmitoyl transferases prevents PKA-mediated inhibition of BK channels. Thus, palmitoylation gates BK channel regulation by PKA phosphorylation. Palmitoylation and phosphorylation are both dynamically regulated; thus, cross-talk between these 2 major posttranslational signaling cascades provides a mechanism for conditional regulation of BK channels. Interplay of these distinct signaling cascades has important implications for the dynamic regulation of BK channels and physiological homeostasis.L arge conductance calcium-and voltage-gated potassium (BK) channels are potently regulated by protein phosphorylation (1) and are important determinants of neuronal, cardiovascular, endocrine, and epithelial function where channel dysfunction may lead to major disorders such as hypertension (2, 3), ataxia (4), epilepsy (5, 6), and incontinence (7). BK channels are potently regulated by phosphorylation, and several putative phosphorylation motifs on the pore-forming ␣-subunit have been identified (8-12). However, as for other potassium channels, the molecular basis through which phosphorylation of the ␣-subunit effects changes in BK channel activity is essentially unknown.BK channel pore-forming ␣-subunits are encoded by a single gene, KCNMA1 (13), and native BK channels show functional heterogeneity in their response to protein kinase A (PKA)-mediated phosphorylation. This diversity results, in large part, from the extensive alternative pre-mRNA splicing of the pore-forming ␣-subunits (10, 12). Previous studies have demonstrated that PKA phosphorylation of a conserved C-terminal phosphorylation motif. RQPS 899 results in BK channel activation (9,10,14). Inclusion of ...

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Overactive Bladder and Incontinence in the Absence of the BK Large Conductance Ca2+-activated K+ Channel

Cited by 310 publications

References 29 publications

Hypercontractility and impaired sildenafil relaxations in the BK_Cachannel deletion model of erectile dysfunction

Hypercontractility and impaired sildenafil relaxations in the BK_Cachannel deletion model of erectile dysfunction

Structure–Activity Relationships of a Novel Group of Large‐Conductance Ca²⁺‐Activated K⁺ (BK) Channel Modulators: The GoSlo‐SR Family

Palmitoylation gates phosphorylation-dependent regulation of BK potassium channels

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Overactive Bladder and Incontinence in the Absence of the BK Large Conductance Ca2+-activated K+ Channel

Cited by 310 publications

References 29 publications

Hypercontractility and impaired sildenafil relaxations in the BKCachannel deletion model of erectile dysfunction

Hypercontractility and impaired sildenafil relaxations in the BKCachannel deletion model of erectile dysfunction

Structure–Activity Relationships of a Novel Group of Large‐Conductance Ca2+‐Activated K+ (BK) Channel Modulators: The GoSlo‐SR Family

Palmitoylation gates phosphorylation-dependent regulation of BK potassium channels

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Hypercontractility and impaired sildenafil relaxations in the BK_Cachannel deletion model of erectile dysfunction

Hypercontractility and impaired sildenafil relaxations in the BK_Cachannel deletion model of erectile dysfunction

Structure–Activity Relationships of a Novel Group of Large‐Conductance Ca²⁺‐Activated K⁺ (BK) Channel Modulators: The GoSlo‐SR Family